John Travolta and Kelly Preston, who announced this week that she's pregnant - at age 47.Steve Granitz/WireImage.com

Kelly Preston and John Travolta announced this week that they’re expecting, sending gossip mags and nail salons into another baby-bump tizzy. Is this a strange Scientology reincarnation? Was it accidental or planned? Will the kid be named Sweathog Jr.?

What nobody thought interesting enough to mention is the fact that Preston is 47.

A generation ago, 47-year-olds kept hard candies in their pockets for their grandkids. Now they regularly puree organic veggies for their newborns before heading out to Mommy and Me yoga. And hardly anyone bats a Latisse-enhanced lash over it.

The now-common sight of a perimenopausal Pampers purchaser would be impossible without the aid of in-vitro fertilization, of course. It is science, after all, that brought us Elizabeth Adeney, the divorced British woman who enjoyed her first Mother’s Day this month at the age of 67. And it is science that seems to be heralding both a dramatic

shift in what we think of as the appropriate age for motherhood, and – potentially – in a seismic redefinition of the purpose of sex.

Dr. John Yovich, an Australian veterinarian who impregnates cattle, recently published a study in the journal Reproductive BioMedicine that predicts IVF will reach a 100% success rate within 10 years. Compare that to the one-in-four chances even the most a hale and hearty young couples have at successfully conceiving the old-fashioned way, and Yovich guesses sex will become largely recreational.

“Natural human reproduction is at best a fairly inefficient process,” Yovich told the Daily Mail. “Within the next five to 10 years, couples approaching 40 will assess the IVF industry first when they want to have a baby.”

Researchers in the US are more circumspect, but they, too, believe that advances in technology will continue to challenge women’s biological clocks – opening the door to childless Baby Boomers and single women who might once have thought parenthood had passed them by.

“Compared to a generation ago, women are clearly delaying childbearing.

In the 1960s, women completed their families by the time they were in their in late 20s,” said Dr. Eric Surrey, medical director of the Colorado Center for Reproductive Medicine.

Back then, the rare pregnant woman over the age of 30 received the clinical label of “elderly” in her medical charts. Not so much anymore.

In the last 20 years, birth rates for women under 30 have dropped. But more women over 30 have been having babies than ever before, with the sharpest increases at the older end of the spectrum – a 47% jump for women ages 35-39 and 80% for women 40-44. In 2008, that worked out to 113,576 babies for women over 40. The average age of new mothers in the US has hit 27 – and continues to creep upward.

Biologically speaking, that’s just not right. Women hit “perimenopause” in their late 30s or early 40s. It’s during that time that eggs start to appear abnormal, decreasing the odds that a woman will successfully conceive. By 42, even fertility doctors say that women essentially hit a wall.

“Where technology has helped us a lot, is in getting better results from using in-vitro, but we can’t really overcome the natural aging process,” Surrey said.

But try telling that to society. The proliferation of books like “Hot Flashes, Warm Bottle: First-Time Mothers Over Forty,” and Web sites like mothersover40.com points to a significant cultural shift in the way society views midlife motherhood.

Some of the credit for this change goes to The Pill. For 50 years since its invention, women have been enjoying more control over their reproductive lives – freeing them up to pursue education and careers.

The more educated the woman, the later in life she tends to marry and have children, according to a recent study by the Pew Research Center.

“Now with women, appropriately, getting more education, we’re seeing many patients ‘trying’ after 30. Personally, I think they’re not shortchanging themselves by waiting until their mid-30s,” to conceive, said Dr. James M. Goldfarb, president of the Society of Assisted Reproductive Medicine, a national membership organization of fertility doctors and clinics.

Single motherhood has also lost much of its stigma. It is now not uncommon for successful, older women (or Angelina Jolie-obsessed unemployed women) to skip the singles bars and head straight to the sperm bank, literally cutting out the middle man.

Society has also come a long way in its perception of fertility medicine. Thirty years ago, “test tube babies,” seemed like science fiction come to life. Goldfarb remembers attending conferences in the 1980s that were heavily fortified with security. These days, the stigma is gone, and IVF and other reproductive medical procedures have changed the way women approach family planning.

“I think there has been a lot of publicity about all the things we can do, and couples tend to ‘try’ for a shorter length of time before they come to a doctor now,” said Goldfarb, who is also director of Infertility and In Vitro at Cleveland Clinic, in Ohio.

While infertility is usually defined as the inability to conceive after a year of unprotected sex, Goldfarb and others say they’re seeing patients – even young ones – come in after just six months for some sex-free intervention.

Still, experts warn that fertility medicine isn’t magic. Despite the success of many women at becoming midlife mommies, it’s hardly a sure thing. Some of the attention paid to high- profile older moms like Claudia Schiffer, 39, and Nicole Kidman, 42, could give women unrealistic expectations. Women see seemingly ageless movie stars pushing strollers, and they forget the realities of aging: menopause can’t be stopped, and eggs decline in quality over time.

“I had a patient come in today at 50 years old,” Goldfarb said. “I had to tell her about how rare it is. We really haven’t accomplished what we’d like. She was disillusioned.”

The national success rate for women over the age of 42 who undergo IVF with their own eggs is less than 17%, compared to 47% for women under 35, according to the Society for Assisted Reproductive Technology.

Goldfarb and others say they are concerned that media attention to cases like Preston’s will result in women thinking they have more time than they actually do.

Particularly since matronly new moms rarely divulge whether they’ve used IVF or other procedures to conceive. These celeb moms also tend to have the means to try more cycles of IVF and other interventions than the average middle-aged woman.

“There are things that simply cannot be changed, like the increase in abnormal eggs,” as women age, Surrey said.

That’s not to say that science isn’t working on a solution for this, too.

One immediate way around the problem is the use of donor eggs – a practice that is slowly becoming more palatable to older would-be moms.

The success rate is pretty great – 55%, regardless of the age of the recipient – but not a lot of people want to admit the baby they’ve carried isn’t biologically “theirs.”

As a result, celebs have not been forthcoming about whether they’ve used donor eggs – though fertility experts’ suspicions and a Talmudic scouring of the pictures in gossip magazines suggest that some celeb moms probably have.

Another sexless solution for old eggs, of course, is straight-up surrogacy, the route Sarah Jessica Parker and Matthew Broderick chose.

For long-term planners, egg freezing is also on the rise, and SART has reported that clinics across the country have been increasingly successful in freezing women’s eggs until they’re ready to use them.

“It does allow a woman in her mid-30s, who [is not ready for motherhood] to be able to make some effort toward preserving fertility,” Surrey said. “If she meets the right person – or doesn’t – and is now in her 40s, she now has eggs from 10 years ago.”

Animal studies have also suggested it is possible to remove the DNA-filled nucleus of a younger woman’s egg and replace it with the nucleus of an older woman’s egg – creating an egg that contains the older woman’s DNA, but the younger woman’s energy-giving cytoplasm.

However, experts warn that some of the younger woman’s DNA remains in the cytoplasm, and the possibility that Heather could really, really have two mommies poses some ethical issues. Not surprisingly, the FDA has not shown much of an interest in approving the procedure.

More realistically, scientists are working to help women combat the clock by helping them to avoid wasting time.

Currently, fertility experts use pre-implantation genetic diagnosis (PGD) to pluck a cell from an embryo and test for a specific genetic abnormality that might prevent an embryo from becoming a healthy baby.

Within five to seven years, experts predict they’ll be able to use a far less invasive procedure that tests the microfluids, or secretions made by an embryo, to determine whether that embryo has a good shot at becoming a healthy baby.

The science is in its, ahem, infancy, but early evaluations look promising, researchers said.

“It could be fantastic to do non-invasive testing on embryos’ metabolism and be able to assure a couple that they would be able to have a healthy pregnancy,” Surrey said.

Of course, experts note that even this advance won’t preserve a woman’s fertility. Not even a famous woman’s fertility.

“We have improved [older would-be mothers’] chances somewhat, but as a profession, we haven’t been able to bump up pregnancy rates in women over 40 even more,” Goldfarb said. “It’s probably our most frustrating problem.”

Goldfarb notes that there seem to be an increasing number of stories of older moms grabbing headlines – but the fact that they keep making the news shows that they’re outliers. We haven’t yet conquered biology.

“There is no reason women in their mid-40s shouldn’t get pregnant. Years and years ago, when women died in their 50s, it made sense biologically” for them not to conceive, Goldfarb said. “But now, a woman who is 45 has another 40-45 years of life expectancy.”

Goldfarb jokes that he has been “trying to campaign nature” to get with the program and allow older women to conceive naturally.

With people living longer, and better, there is no reason the oldest mother of all – Mother Nature – shouldn’t give the Medicare set a green light to have babies the old-fashioned way, by bumping walkers.

“There’s something nice about conceiving naturally,” said Goldfarb, a man. “I think a vast majority of people would want to try on their own first.”

But until Mother Nature decides to bend the rules for all of us, science will continue to try to make it possible to outwit biology.